| 瑶岗仙“五层楼”式脉钨矿床围岩蚀变研究 |
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| 引用本文：.1984.Wall Rock Alterations Of A "Fi've-Storied" Vein-Type Tungsten Deposit At Yaogangxian, Hunan Province[J].Mineral Deposits,3(2):68~75 |
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| Wall Rock Alterations Of A "Fi've-Storied" Vein-Type Tungsten Deposit At Yaogangxian, Hunan Province |
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| Abstract:The "five-storied" zoning of the vein-type tungsten deposit with its related regional multistage mineralizations has formulated a new topic in the study of wall rock alterations, at various "ore-forming stages. Statistics of hundreds of tungsten deposits of various sizes show evidently that large- and medium-sized ore bodies occur mainly in the excontact zone of granite. It is desirable, therefore, to look into wall rock alterations of the "five-storied" vein-type tungsten deposits present mainly in sedimentary sequences. The "five-storied" vein-type tungsten deposit at Yaogarrgxian is an exocontact zone deposit formed for its main part at the fifth ore-forming stage. The near-ore wall rocks are in upward succession mica-hornfels, sericite-metamorphic sandstone, weakly metamorphic sandstone, sandy shale, etc. Based on detailed field observations and laboratory data, this paper dwells on types of near-ore alterations related to the fifth mineralization stage with a description of horizontal and vertical zoning of the altered, rocks. From the vein outward or from the bottom upward, alterations change .gradually from sericitization to silicification. The distribution of minor elements in altered rocks corresponds to alteration zoning. Evidently lots of arsenic was brought to the altered rocks above the vein zone, forming as a result a significant amount of arsenopyrite. This serves as an indicator in search for ore deposits of this type. Variations in altered minerals, chemical composition and minor elements all point to a progressive transition nature of the zoning, suggesting that the alteration zoning resulted mainly from concentration gradient of ore-forming fluids and variation in acidity of the media. Apparent change in width of alteration zone, i. e., varying from narrow to broad, can be observed from the depth upward, presumably caused by porosity of the wall rocks and pressure gradient between the ore-forming fluids and the wall rocks. This furnishes a fairly reliable symbol indicating hidden or concealed ore deposits. A detailed discussion is also given in this paper concerning evolution of hydrothermal fluids and relationship of alterations to mineralization. |
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